The long term objective of the research described in this application is to elucidate structure-function relationships in inner ear sensors. These relationships are expected to be rich in implications regarding the physical mechanisms employed in signal processing. A thorough understanding of the relationship between sensor structure and function is necessary so that the underlying mechanisms of inner ear pathologies might be understood and rational measures undertaken to alleviate them. Inner ear sensors process a variety of incoming sensory signals including airborne auditory, substrate-borne seismic and internally generated signals concerning the position and movement of the head in space The proposed study focuses on the innervation of two of these sensors; the basilar papilla, an auditory sensor and the lagenar macula, a vestibular/seismic sensor. The animal models to be used in this study are the red-eared turtle (Pseudemys scripta elegans), and two geckos (Gekko gecko and Coleonyx variegatus). The structural and functional similarities between lower vertebrate sensors and that of mammals has resulted in substantial contributions to the understanding of inner ear sensory cell biophysics of peripheral signal processing. Information provided in these studies has also done much to clarify our understanding of the evolution of inner ear sensory cell biophysics and peripheral signal processing. Information provided in these studies has also done much to clarify our understanding of the evolution of inner ear sensors and therefor our appreciation for the basic elements necessary to perform auditory and vestibular tasks. The focus of this proposal is to provide quantitative fine- structural information with particular attention paid to the existence and pattern of neuronal microcircuits which may contribute to peripheral signal processing. Two major questions will be addressed; 1) What are the innervation patterns in various regions of these sensors? And 2) What are the quantitative differences in neuronal synaptic contacts in these regions? Sensor morphology will be studied with transmission electron microscopy of serial sections from which three-dimensional reconstructions of both sensory cells and neuronal processes will be derived. The principal investigator is trained and published in the methods required to complete the goals of the proposed research.